My J117 Espace from 1987 is suffering from unstable idle. Revs dip periodically, if I'm driving at low speed the engine may stop, and then it's impossible to start until it's become cold again (took me 20 minutes last week!)

I've fixed the problem by turning the idle screw on the throttle valve housing allowing enough air to pass outside the valve to keep the revs so high that they don't dip.

I've been looking for air leaks in the inlet manifold, with no success. I've been hearing a sound from there that could be an air leak, but is probably the noise the fuel pump is making in the fuel.

Could it be my lambda-sensor (oxygen sensor)?

I have a very bad engine electrical system and plan to replace the wirering (sensors seem okay), but I have checked it all through recently, and it seems to work.

It's not the lambda sensor! This evening I connected an oscilloscope to the lambda sensor, and after the initial startup of the engine, the voltage starts switching between 0V and 0.62V with a period of a couple of seconds.

Although it's good to investigate the problem yourself, have you had a check with a diagnostic computer?

It doesn't have to be the official Renault one, any garage with modern facilities should be able to plug your car in and give you some clues to finding the problem very quickly. The Espace on board computer stores every problem occurring until its been downloaded and cleared.

I recently had a problem with my 24v Espace, running like a Murena with a Solex carburettor full of dirt! It turned out to be a leaking rocker cover gasket dripping oil on to one of the ignition wiring connectors.

It's not the lambda sensor! This evening I connected an oscilloscope to the lambda sensor, and after the initial startup of the engine, the voltage starts switching between 0V and 0.62V with a period of a couple of seconds.

I guess that should be on my list. Thanks for reminding me. The computer *is* asking for a download of fault codes, but when I got the car, the wire to the water temp sensor was broken, that's probably the fault it's wanting to tell us about.

I don't think the computer can see an air leak or a too low fuel pressure, do you?

Could you see the dripping oil on the computer screen? (just kidding!)

I owned a Volvo 480 with fuel injection for many years and had recurring problems with unstable idle.

The fuel injection diagram had something called the "idle speed regulating valve" which looked like a clue. It opens and closes to regulate the amount of air at idle and control the idle speed. It was prone to clogging up (enough to stall the engine, or make it race at idle) and I got used to cleaning it out with "carb cleaner" spray. Eventually I got fed up and fitted a new one -- that cured the problem permanently.

Out of interest I took apart the old valve -- it consisted of an armature (like a motor) inside a magnet. The clearance was very small indeed and the armature was rusty, so it was sticking.

A quick Google check reveals this is a known problem on Espaces too -- see http://dinsen.net/espace/teknik/j11-j63/fuelinjection. Quote "One frequently encountered source of problems with this engine is the idle speed valve." He then goes on to describe your symptoms.

Hi Anders -- I doubt a visual check is conclusive. Mine [when faulty] still worked but because it was sticky it didn't pass the correct amount of air. And yes I think it was the same engine as yours -- that sodding idle valve certainly looks familiar!

But I'd strongly endorse the other replies that suggest a computer diagnosis -- there's a host of other possibilities.

Hi Anders -- I doubt a visual check is conclusive. Mine [when faulty] still worked but because it was sticky it didn't pass the correct amount of air. And yes I think it was the same engine as yours -- that sodding idle valve certainly looks familiar!

Hmm, you are probably right. I sprayed wd40 in the valve. It did actually change the behaviour and idle speed was lowered slightly...

I have a 1996 espace and I had the idle speed vavle replaced by a spare part (not new) The old one was simply failing to open/close. This one I now have operates perfectly when the engine is at running temp. but it is erratic and stalls when cold. I have a friend at work who replaced this part on his espace with a new one at he still has the idle speed problem. I had previously (with the old idle valve on) had the car checked by computer at the garage and they said I needed the valve changing but nothing else was faulty. Now I just have the idle speed raised a bit so it doesn't stall so much. What else causes this problem?

I have a 1996 espace and I had the idle speed vavle replaced by a spare part (not new) The old one was simply failing to open/close. This one I now have operates perfectly when the engine is at running temp. but it is erratic and stalls when cold. I have a friend at work who replaced this part on his espace with a new one at he still has the idle speed problem. I had previously (with the old idle valve on) had the car checked by computer at the garage and they said I needed the valve changing but nothing else was faulty. Now I just have the idle speed raised a bit so it doesn't stall so much. What else causes this problem?

Thanks

Check for bad sensors, especially the water temperature sensor. Also air leaks in the inlet manifold may cause unstable idle. Check the fat pipe running from the engine top to the manifold. But since it's only when it's cold, check the water temperature sensor first and make sure you measure it by the computers connections to ensure that the wirering is okay.

Water temp. sensor. I expect this can only be checked via one of those computer thingies? I think that is going to have to wait for now. However, as you suggest, it does seem to follow a logical course. I have recently had all the inlet manifold gaskets replaced so that is most likely ruled out. I appreciate your advice and suggestions. I have also left a post regarding fuel and would value your feedback on that, too. Cheers Anders.